Simonson (1958) proposed that soil formation could be regarded as two major steps:

  • The accumulation of the parent material
  • The differentiation of the horizons within the soil profile by soil-forming processes, which can be categorized as:
    • Additions
    • Removals
    • Transfers or translocations of materials
    • Transformations

All processes are active to some degree in all soils. The balance between the combination of processes determines the ultimate nature of the soil profile.

Soil forming processes
Some of the major processes of soil formation within a pedon are summarized in the following table (Adapted from Buol et al., 1980. Soil Genesis and Classification. The Iowa State University Press, Ames).
ProcessCategoryBrief Description
Eluviation Transfer Movement of material out of a horizon
Illuviation Transfer Movement of material out of a horizon
Decalcification Transfer Reactions that remove CaCO3 from a horizon
Calcification Transfer Processes leading to accumulation of CaCO3
Desalinization Transfer Removal of soluble salts in a horizon
Salinization Transfer Accumulation of soluble salts in a horizon
Solonization Transfer Accumulation of sodium salts in a horizon
Solodization Transfer Leaching of sodium salts from a horizon
Leaching Transfer Removal of soluble material from the soil
Lessivage Transfer Physical transfer of clay within the solum
Pedoturbation Transfer Physical churning and mixing of soil material
Podzolization Transfer Chemical migration of iron, aluminum, and SOM within the solum
Gleization Transfer Reduction of Fe3+ to Fe2+ under anaerobic conditions and transfer of Fe2+
Desilication Transfer Chemical migration of silica out of the solum leaving iron and aluminum minerals behind
Melanization Transfer Darkening of A horizon material by addition and mixing of SOM
Decomposition Transfer Breakdown and loss of minerals and SOM
Mineralization Transfer Release of inorganic material through decomposition of organic matter
Paludization Transfer Accumulation of organic materials under anaerobic conditions (Organic soils)